I have a problem with my hall and landing lighting. Downstairs is a two switch light fitting, upstairs landing is a one switch fitting. The downstairs light has two sets of wires supplying power to the switches, each wire carries one red and one black wire. the light fitting has two gangs labelled "L" at the top and "L1" bottom left "L2" bottom right. I have tried to wire the switches as per the lighting diagram which came with the switches but I'm having problems. I can get the downstairs only working via gang one, red wire in "L" and black wire in "L2", but no matter how I wire the other gang and the upstairs switch I cannot get the upstairs working. I need to wire upstairs so that it can be switched on and off using both switches upstairs and downstairs. The below drawing shows the set up, can somebody please let me know how to wire these switches so both lights work. nb the old wiring system had a small 2inch red 'flywire' but I'm not sure what this was for.

You will not get it to work following instructions as this method is no longer used. The problem is it can cause interference to other equipment and also can cause problems if one wants a separate fuse/MCB up-stairs and down stairs.

With a normal 2 way switch using labels you give the main switch will have the two switch wires going to L1 and L2. There will then be a three core cable which connects the two switches like for like. So if the blue is L1 on one switch it will be L1 on other switch of the pair.

Either L1 or L2 will be permanent line and years ago to save using 3 core on the second switch of the pair they would link the permanent line from the adjacent switch to the two way switch this could be L1 or L2.

So first switch will have four wires. Line (often red) will go to either L1 or L2 on it's own. Switch return (often black paired with above) will go to the other terminal not used by line either L1 or L2.The first wire in the cable between both switches will go to L (Called Com on some switches) and the second wire will go to same terminal as switch return. [Could be either L1 or L2]

The second switch will have just two wires the one going to L on other switch must also go to L on second switch. Normally we will also match up the second wire so if L2 at one switch also L2 at second but not so important. The empty terminal be it L1 or L2 then is linked to the line of adjacent switch.

The first switch will not work without the second switch being connected.

This practice of using just two wires has become a problem of late because over the years it has become common to split up-stairs and down-stairs supplies to lights. If this is done where there are only two wires in the strapper then it becomes what is known as a borrowed neutral which is dangerous. This may have gone on unnoticed for years until a consumer unit with RCD protection is fitted. At which point the RCD will trip when the switches are in one (not both) of the on positions. As a result electricians have three ways.

1 Rewire2 Remove two way lighting3 Combine upper and lower floors back to same MCB.

So I would consider before you next decorate you get the wires changed to three core so if you upgrade to RCD protection you don't have this problem. It will also stop problems with telephone wires picking up mains hum and messing up broad band.

Although I have not seen it done that way I know you can take the wires vie the ceiling rose. I would guess that is what has happened in your case.

Assuming that then the simple way is to work out which is the live supply to the non two way switch and bridge this to either L1 or L2 on two way switch which ever is not being used. Cross fingers I hope it works as other wise it's a full tracing job.

I have also had problems linking to pictures and putting pictures on this forum. It will not work with some formats even if to try to upload and I am not spending ages playing with them. Far easier to just move to a forum which will take links and all common picture types.

My own web site has all the diagrams I need but this forum will not allow me to link to them.